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.68                           METALLUEGY OF IRON AND STEEL.
tributions he compared* the working of a typical Pittsburg furnace with the practice in the Cleveland district in England. In Tables II-B and II-C the results are tabulated and expanded, so as to show the way the heat is utilized under two entirely different sets of conditions.                                                                                 ,
In Table II-C I have departed from his line of calculation in finding the equivalent amount of coke in the American furnace. The. object of the investigation is to account for the larger amount of fuel used in England, and Bell sums up every way in which the lean and silicious ores of Cleveland increase the work to be done; but although he mentions that Connellsville coke contains more ash than the coke of Durham, he makes no allowance for this .at all. The furnaeeman cannot get calorific power out of this ash, and for this reason I believe that the calculation by Bell on the heat developed per unit of coke (p. 958 loc. cit.) is entirely misleading. The. difference of 7.00 per cent, (not "7-J per cent.") is accounted for by the extra ash which the American coke contains, for Durham coke is given as 5 to 7-J per cent, in ash, while Connellsville will run at least 5 per cent, higher.
The composition of the gases from the Cleveland furnace is not given, but the ratio is recorded and the weight produced per ton of iron, and from, these data. I have calculated the composition. Bell views the gases simply as a vehicle of sensible heat, with the exception of the calorific power returned in the blast, but I believe it more correct to calculate all the potential energy in the coke and find how much is accounted for, either as potential or chemical energy, or as sensible heat. Pell did this in previous writings and showed that in one case 74 per cent, of the heating power of the fuel was employed in useful work, but this counted the energy developed in boilers and hot stoves. I believe it is better to keep this energy separate under the name of "potential heat in gas," as the economical use of such gas is a problem entirely distinct from the metallurgy of a blast furnace. Table II-D gives the total1 heat developed in the furnace and the distribution of this heat.
The potential, heat includes all the energy of the escaping gases, except the sensible heat.  It appears later in four places:
'   '"              ""     :         * Trans. A, I. M. IB., Vol. XIX, p. 957.         '